Health A-Z

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Harvard Medical School

Sore Throat (Pharyngitis)

What Is It?

A sore throat, also called a throat infection or pharyngitis, is a painful inflammation of the pharynx — the back portion of the throat that includes the back third of the tongue, the soft palate (roof of the mouth) and the tonsils (fleshy tissue that are part of the throat's immune defenses). The most common cause of sore throat is infection with bacteria or a virus.

Because an infection of the pharynx almost always involves the tonsils, tonsillitis (inflammation of the tonsils) was once a common name for infectious pharyngitis.

Currently in the United States, infectious pharyngitis accounts for almost 10 million visits to doctors' offices each year, and sore throat is among the top 10 complaints of people who seek treatment in emergency rooms. In about 85% of cases, throat infection is caused by a virus. Although people who have the flu (influenza), cold sores (oral herpes simplex) or infectious mononucleosis ("mono") also commonly have a sore throat, these viral infections usually cause other telltale symptoms in addition to throat pain.

In regions that have warm summers and cool winters, viral pharyngitis typically peaks during the winter and early spring, a time when people often are close together in poorly ventilated rooms. In this environment, the viruses that cause pharyngitis spread easily in the droplets of coughs and sneezes and on dirty hands that have been exposed to fluids from a sick person's nose or mouth. In most people who are otherwise healthy, simple viral pharyngitis doesn't last long, goes away on its own and does not causes any long-term complications, although the short-term discomfort can be significant.

In cases of infectious pharyngitis that are not viral, the cause is almost always a bacterium — usually a group A beta-hemolytic Streptococcus, which causes what is commonly called strep throat. Like viral pharyngitis, strep throat can spread quickly and easily within a community, especially during late winter and early spring. Unlike most forms of viral pharyngitis, however, untreated strep throat can lead to serious complications, such as glomerulonephritis (a kidney disorder) and rheumatic fever (a potentially life-threatening illness that can damage heart valves). A strep infection also has the potential to spread within the body, causing pockets of pus (abscesses) in the tonsils and in the soft tissue around the throat.